Rotary drums



F. R. MADSEN Aug. 25, 1964 ROTARY DRUMS 5 Sheets-Sheet 1 Filed Aug. 9,1962 FIG. 1

7 2:221; 72* M iMf W F. R. MADSEN Aug. 25, 1964 ROTARY DRUMS 3Sheets-Sheet 2 Filed Aug. 9, 1962 FIG. 4

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ATTORNEY5 INVENTOR F. R. MADSEN Aug. 25, 1964 ROTARY DRUMS 3Sheets-Sheet 3 Filed Aug. 9, 1962 United States Patent 3,145,979 ROTARYDRUMS Frederik Rmclre Madsen, Copenhagen, Denmark, assignor to F. L.Smidth & C0., New York, N.Y., a corporation of Delaware Filed Aug. 9,1962, Ser. No. 215,987 6 Claims. (Cl. 263-33) This invention relates torotary drums and, in particular, to drums provided with conveyer flightsand drying chains.

Rotary drums are often used to dry or preheat a slurry of raw mineralmaterial which is to be burned, typical sluiries being those of cementraw materials, lime, and Mesa, which is a spent lime material producedin the paper industry. Rotary drums used for such purposes are generallypart of a rotary kiln but may be independent structures. In such a drum,the slurry is heated by hot kiln gases evolved in the kiln as the slurryand the gases travel in opposite directions through the drum. The slurryis moved through the drum by tilting the drum and the drum may also beprovided on its inner surface with conveyer flights of helical formwhich, on rotation of the drum, pick up the slurry and move it axiallythrough the drum.

The heat exchange between the hot gases and the slurry in a simplerotary drum is inefficient, because the gases can only give up theirheat to the walls of the drum and to the surface of the slurry.Accordingly, to improve the operation, lengths of chain are oftensuspended inside such drums to increase the surface area of the slurrysubjected to the drying gases. Such chains may be secured at one end torings on the interior of the drum so that, during rotation of the drum,a number of chains will hang in groups to form curtains across the drum,while other chains on the diametrically opposite side of the ring willrest on the bottom of the drum in the slurry. Each chain lies within theslurry when it rests on the bottom of the drum and, when the drum isrotated, the chain lifts the slurry adhering to it and thus exposes theslurry coating on the chain to the hot gases in the middle of the drum.

In rotary drums having both conveyer flights and chains, the conveyerflights conveying the slurry and the chains exposing the slurry to thehot gases act independently of each other in that the conveyer flightshave little eflect on the movement of the chains in the drum and thechains have little eflect on the movement of the slurry by the conveyerflights. The reason is that the conveyor flights in such drums arenarrow and of a width generally less than or at most 12%, of theinternal diameter of the drum, so that a chain, which rests on a flightat the bottom of the drum soon hangs free and out of contact with theflight as the drum rotates.

Slurry is removed from a chain in such drums when the chain rubs againstother chains during the rotation of the drum but slurry can be stickyand, when it is in such a condition, it cannot readily be removed from achain, to which it adheres. With such slurry, the chains and flights inthe drums soon become heavily coated and, in some instances, individualchains may stick together when hanging suspended in the drum. The resultis that the coated chains obstruct the free flow of gases through thedrum and the efliciency of heat exchange between the hot gases and theslurry is impaired, since the slurry coating on the chains is notconstantly renewed. In addition, the slurry in such drums tends toadhere to the conveyor flights and does not move readily through thedrum.

The difliculties encountered in the drying and preheating of slurry inrotary drums as heretofore constructed are overcome in a drum embodyingthe present invention. In the new drum, the width of the conveyorflights, the

3,145,979 Patented Aug. 25, 1964 pitch of the helix formed by eachflight, and the length of the chains are so co-ordinated that, on eachrevolution of the drum, a substantial length of each chain slides andrubs over part of the surface and the edge of at least one flight. As aresult, the slurry is scraped from both the chains and the surface ofthe flights, and an undesirable accumulation of slurry on the chains andflights is prevented.

The dimensions of a rotary drum embodying the invention vary with thesize of the rotary kiln, with which it is used or of which it forms apart, and depend to some extent on the composition of the slurry to betreated. However, it is preferable to use flights which make an anglebetween 40 and with the generatrix of the drum and have a width ofbetween 12% and 45% of the interior diameter of the drum. The length ofthe chains may then vary between 50% and of the internal diameter of thedrum. The chains are so arranged that they extend in a plurality ofgroups to form curtains lying in radial planes which are axially spacedalong the length of the drum and, in addition, a flange may be attachedto the edge of each flight to improve the scraping eflect between thechain and flight when a chain slides over the edge of the flight.

A preferred embodiment of the invention is shown in the accompanyingdrawings, in which FIG. 1 is a cross-sectional view of a rotary drumshowing the disposition of the groups of chains;

FIG. 2 is a fragmentary longitudinal sectional view on the line 2-2 ofPEG. 1 with chains omitted;

FIGS. 310, incl., are diagrammatic views similar to FIG. 1 showing thepositions of a single chain at different stages during a rotation of thedrum; and

FIG. 11 is a fragmentary perspective view of a modified conveyor flight.

In the drawings, the rotary drum 1 is shown as forming an integral partof a kiln, in which the slurry moves toward the right in FIG. 2 and thehot gases move in the opposite direction. The drum has a cylindricalsteel casing 2 with a refractory lining 3 and includes a section 4containing the conveyer flight 5 and chains 6 of the invention and asection 7 free of chains. The section 7 extends to a zone 8 containingconventional drying chains 9 connected at both ends to the wall of thedrum. The drum is provided with a plurality of rings 10 secured to theinterior of the drum to lie in spaced planes normal to the drum axis andthe chains 6 are secured at one end to the rings in spaced relation andthus hang free vertically to form a curtain ll, when that part of thering to which they are attached is at the top of the drum.

The rings 10 are so disposed that the chain curtains 11 are axiallyspaced along the drum, preferably between 4" and 24", depending on thesize of the drum and the properties of the slurry being treated. Theflights may project beyond the chains at either end or both ends of thechain section and the distance, through which the flights project, maybe as much as the diameter of the drum. The points of attachment of thechains are spaced apart 2 to 8 inches on each ring except that a chainmay be omitted, where a flight intersects a chain curtain. Additionalchains may be omitted to form gaps in one or more curtains to regulatethe flow of gas through the drum.

The flights may extend beyond the last curtain 11 approximately half-wayacross the zone 7 towards the drying zone 8 and, if desired, may extendentirely through the zone '7. The width of the flights shown in FIGS. 1and 2 is approximately 20% of the interior diameter of the drum and, asa general rule, the width may vary between 12% and 45% of the internaldiameter depending on the drum size and the slurry being treated in thedrum. Also, while the drum 1 is shown as being provided with sixflights, it is to be understood that the number of flights used isconveniently from 4 to 10 with the number varying according to the drumsize and with large drums usually having more flights than small drums.

The length of the chains shown in FIG. 1 is approximately 75% of theinterior diameter of the drum. However, the length of the chains mayrange between 50% and 150% of the internal diameter of the drum with theactual length determined by such factors as the width of the flights andthe number of flights used. Thus, in a drum having six flights of awidth about 20% of the internal diameter of the drum, the length of thechains may advantageously be about 75% of the diameter.

The movement of a single chain 6 as the drum is rotated may be readilyunderstood by reference to FIGS. 3-10. In explaining the movement of thechain, the flight immediately behind that part of the ring 10, to whichthe chain is attached, will be referred to as the central flight and theflights on opposite sides of the central flight will be referred to asthe rear flight and the front flight, respectively.

In FIG. 3, the chain 6a is shown hanging vertically from its ring 10,which is at the top of the drum, and the chain is obstructing the flowof gases and the chain and its slurry coating are being heated or dried.The group of chains depending from the ring 10 form a curtain 11.

When the drum is rotated approximately an eighth of a revolution in aclockwise direction, as shown in FIG. 4, the chain will assume aposition, in which it no longer hangs directly across the path of thegases, and Will come into initial contact with the central flight 5a andthe rear flight 5b, although there has been little relative movementbetween the chain and these flights.

Further rotation will cause the chain to take the position shown in FIG.5, and, in reaching that position a substantial length of the chain willhave slid and scraped across the edges of the central and rear flights5a, 5b. The result of the sliding and scraping is that slurry will beremoved from the chain and the edges of the flights, on which the chainslides.

Further rotation of the drum through an eighth of a revolution to theposition shown in FIG. 6 does not move the chain significantly relativeto the central flight 5a but the chain begins to slide back across theedge of the rear flight 5b into the space between the flights 5a and 5b.In this position, the chain picks up fresh slurry from the bottom of thedrum.

Further rotation through an eighth of a revolution to the position shownin FIG. 7 causes the chain to slide back along the edge of the flight 5buntil most of the chain lies between the flights 5a and 5b. The movementof the chain from the position shown in FIG. 6 to that of FIG. 7 causesfurther scraping of slurry from the chain and the flights.

When the drum rotates so that the chain takes the position shown in FIG.8, the chain continues to slide into the space between the flights 5aand 5b and the part of the chain hidden from view will sweep over asubstantial area of the flight 5a to remove slurry from it and advancethe slurry through the drum. Still further rotation of the drum willcause the chain to take the position shown in FIG. 9, in which the chainwill have swept over a further area of the flight 5a.

As the drum continues to rotate, the chain reaches the position shown inFIG. 10, in which it hangs in contact with the edge of the forwardflight 5c.

During the rotation of the drum, a chain does not remain in the plane ofthe curtain, of which it forms a part. Thus, in moving from the positionshown in FIG. 3 to that shown in FIG. 4, the chain is pushed forwardtoward the mouth of the drum by the flight 5a. During the later stagesof the revolution of the drum, the chain slides out of the plane of thecurtain in the opposite direction. This may be seen in FIG. 2 where thechains 6a and 6b extend down part of the surface of the flight, withwhich they are in contact, and are displaced to the right of the planeof the curtain.

In operation of the rotary drum shown in FIGS. 1 and 2, there is at alltimes a mass of chains slidiing along the surfaces of the flights 5a and5b and the weight of the chains insures that the slurry will be freedfrom the surfaces of the flights. During a complete revolution of thedrum, a chain is scraped by the edges of flights both during thedownward part of a revolution of the drum and also during the upwardpart. The sweeping action of the chains along the surface of theflights, however, only takes place when the chains are moving in anupward direction.

A modified form of conveyor flight is shown in FIG. 11 as including aflange 12 secured to the inner edge of the flight 13 to lie normal tothe flight. Such a flange improves the scraping action as a chain slidesover the edge of the flight.

I claim:

1. A rotary drum having a plurality of axially extending conveyorflights of helical form, mounting means within the drum, and a pluralityof chains each secured at one end only to the mounting means between theflights, characterized in that the length of each chain is between 50%and 150% of the internal diameter of the drum, the width of each flightis between 12% and 45% of th internal diameter of the drum, and theinterior of the drum inward from the free edges of the flights is open.

2. The drum of claim 1, in which each flight forms an angle between 40and with the generatrix of the drum.

3. The drum of claim 1, in which the chains are arranged in groups toform a plurality of curtains hanging in respective radial planes spacedaxially along the drum.

4. The drum of claim 3, in which the curtains are spaced between 4 and24 inches.

5. The drum of claim 3, in which the points of attachment to the drum ofthe chains of each group lie in a plane normal to the axis of the drumand the points are spaced from 2 to 8 inches.

6. A rotary drum for treating a cement raw slurry and having a pluralityof helically shaped conveyor flights and a plurality of chains eachattached at one end only to the interior of the drum, characterized inthat the drum has at least six conveyor flights each of a width between12% and 45% of the internal diameter of the drum, with each flightmaking an angle with the generatrix of the drum between 40 and 80, andeach chain is of a length between 50% and of the internal diameter ofthe drum, the chains are arranged in groups to form curtains lying inradial planes with adjacent curtains spaced between 4 and 24 inches, andthe points of attachment to the drum of adjacent chains in a group liespaced between 2 and 8 inches.

References Cited in the file of this patent UNITED STATES PATENTS2,001,227 Vogel-Jorgensen May 14, 1935 2,230,601 Puerner et al Feb. 4,1941 FOREIGN PATENTS 473,553 Great Britain Oct. 14, 1937 881,927 GermanyJuly 6, 1953 1,017,007 France Sept. 10, 1952

1. A ROTARY DRUM HAVING A PLURALITY OF AXIALLY EXTENDING CONVEYORFLIGHTS OF HELICAL FORM, MOUNTING MEANS WITHIN THE DRUM, AND A PLURALITYOF CHAINS EACH SECURED AT ONE END ONLY TO THE MOUNTING MEANS BETWEEN THEFLIGHTS, CHARACTERIZED IN THAT THE LENGTH OF EACH CHAIN IS BETWEEN 50%AND 150% OF THE INTERNAL DIAMETER OF THE DRUM, THE WIDTH OF EACH FLIGHTIS BETWEEN 12% AND 45% OF THE INTERNAL DIAMETER OF THE DRUM, AND THEINTERIOR OF THE DRUM INWARD FROM THE FREE EDGES OF THE FLIGHTS IS OPEN.